The present invention relates to the provision of a prosthesis material for use with a living body, the material possessing biocompatibility and blood compatibility. The invention includes a method for the manufacture of such material.
Vascular prostheses made of porous fabrics such as expanded polytetrafluoroethylene (Teflon.RTM.) and woven or knitted polyethyleneterephthalate (Dacron.RTM.), although successful in the replacement of large-diameter arteries, have not proven useful for long-term applications as venous or small-diameter arterial substitutes.
Numerous techniques have been described in the prior art to produce porous or filamentous small-diameter tubular fabrics from polymers. For example, White and co-workers in Science, 1972, 176, pages 922-924 and Arch Surg., 1979, 114, page 698 reported a replamineform template process using calcite derived from sea urchin spines. The spines were machined into tubes of the desired diameter and wall thickness and then pressure-injected with a polyurethane solution. Following solvent evaporation, the calcite was dissolved with hydrochloric acid, leaving a polymer wall structure with interconnected pores. Lyman et al. in Trans. Am. Soc. Artif. Intern. Organs, 1977, 23, pages 253-260 reported a technique for producing porous, compliant prostheses using repeated cycles of dipping a glass mandrel in a copolyetherurethane-urea using N,N-dimethylformamide (DMF) as a solvent, and precipitation in water. Annis et al. in Trans. Am. Soc. Artif. Intern. Organs, 1978, 24, pages 209-213 reported the preparation of filamentous polyurethane tubes by electrostatic spinning. In this process, a highly porous and distensible non-woven fabric was formed by ejecting a polymer solution from a syringe onto a sliding, rotating steel mandrel through an electrostatic field obtained by maintaining the mandrel at -20 kV. Leidner et al. in J. Biomed. Mater. Res., 1983, 17, pages 229-247 disclosed the extrusion of a polymer in the liquid phase (either melted or dissolved in a solvent) through fine orifices to form fibers which could be stretched and wound onto a rotating mandrel. Prosthesis material has also been produced by a method wherein: 1) a polymer solution in a mixed solvent is formed by bringing a polymer solution near its precipitation point by the addition of a nonsolvent; 2) a substrate is coated with this so-form solution and 3) a porous structure is formed by evaporating at least part of the solvent fraction of the mixed solvent. (See Gogolewski et al, PCT published application WO86/0204, International Application No. PCT/SE85/00420, published on May 22, 1986). Recently, Kowligi et al. in J. Biomed. Mater. Res., 1988, 22 A3, pages 245-256 described a spraying technique to apply a fine mixture of polymer solution and nitrogen gas bubbles onto a rotating mandrel.
It is an object of the present invention to provide a new and flexible approach for the fabrication of membranes, especially tubular membranes, suitable as prostheses, especially vascular prostheses, most especially a small diameter vascular prosthesis.
It is further object of the present invention to provide a small diameter highly porous tubular membrane vascular prostheses which shows a high degree of patency and which does not induce anastomotic hyperplasia.
A still further object of the present invention is to provide a highly porous membrane prostheses, especially in small diameter tubular form, which promotes minimal connective tissue growth on the luminal surface to support the formation of a thin, stable, mature neointima and which enhances completeness of the healing process.
A yet further object of the present invention is to provide a process for the preparation of porous membranes which is relatively simple, flexible and reproducible.